Control device for a power system for driving a hydraulic fluid actuated motor

ABSTRACT

A COMPRESSED AIR MOTOR DRIVES A HYDRAULIC FLUID PUMP WHICH SUPPLIES A HYDRAULIC FLUID MOTOR WITH DRIVE FLUID. A MOTOR ACTUATED VALVE SENSES THE PRESSURE AND FLOW OF THE HYDRAULIC FLUID AND CONTROLS THE SUPPLY CONDUIT OF THE AIR MOTOR SO AS TO LIMIT INDIRECTLY ON THE ONE HAND THE PRESSURE OF THE HYDRAULIC FLUID AND ON THE OTHER HAND THE FLOW OF THE HYDRAULIC FLUID.

Dec. 14, 1971 N, J S N 3,626,695

CONTROL DEVICE FOR A POWER SYSTEM FOR DRIVING A HYDRAULIC FLUID ACTUATED MOTOR Filed March 30, 1970 2 Sheets-Sheet 1 Fig. I

I I I5 I4 Fig.2

N. G. JONSSON 3,626,695 CONTROL DEVICE FOR A POWER SYSTEM FOR DRIVING Dec. 14, 1971 A HYDRAULIC FLUID ACTUATED MOTOR 2 Sheets-Sheet I Filed March 30, 1970 INVENTOR. 'finsa'o,

IV S G BY United States Patent *O-ce 3,626,695 CONTROL DEVICE FOR A POWER SYSTEM FOR DRIVING A HYDRAULIC FLUID ACTU- ATEI) MOTOR Nils Gunnar Jonsson, Jakobsberg, Sweden, assignor to Atlas Copco Aktiebolag, Nacka, Sweden Filed Mar. 30, 1970, Ser. No. 23,750 Claims priority, application Sweden, Apr. 3, 1969, 4,859/ 69 Int. Cl. F1611 31/00 US. Cl. 60-53 R 9 Claims ABSTRACT OF THE DISCLOSURE A compressed air motor drives a hydraulic fluid pump which supplies a hydraulic fluid motor with drive fluid. A motor actuated valve senses the pressure and flow of the hydraulic fluid and controls the supply conduit of the air motor so as to limit indirectly on the one hand the pressure of the hydraulic fluid and on the other hand the flow of the hydraulic fluid.

This invention relates to a control device for a power system for driving a hydraulic fluid actuated motor, the power system comprising a hydraulic fluid pump which is driven by a compressed air actuated motor and supplies a flow of hydraulic fluid to a hydraulic fluid conduit which is the supply conduit of a hydraulic fluid actuated motor.

Power systems of this type are used in cases when electric motors for driving hydraulic fluid pumps are unsuitable or cannot be used at all. This is often the case in connection with hydraulic fluid actuated drilling machines for underground use.

However, the characteristics of an air actuated motor do not adapt themselves to the characteristics of a hydraulic fluid pump, because, on the one hand, an idling air motor can run at high speed while a hydraulic pump cannot stand excessive speed and, on the other hand, when an air motor is loaded, the speed decreases simultaneously with the torque increasing substantially while the pressure of the hydraulic delivered from a hydraulic fluid pump of the positive displacement type is proportional to the torque applied to the pump. The consequence is that a hydraulic fluid pump being a part of a power system as described, cannot be adapted to have its displacement decreased automatically in response to a rise in the pressure of the delivered hydraulic fluid; a control arrangement which is commonly used in connection with bydraulic fluid pumps of the axial piston type driven by electric motors. Therefore, neither the hydraulic fluid pump nor the hydraulic fluid actuated motor in a power system, as described, can be used at maximum efliciency because the maximum flow and maximum pressure do not appear simultaneously at the inlet of the fluid motor and because the increase in pressure at increasing load and the increase in flow at decreasing load must be permitted.

An object of the invention is to eliminate these disadvantages and to provide a power system comprising a hydraulic fluid motor actuated by means of a flow of hydraulic fluid delivered from a pump driven by means of a compressed air operated motor, in which power sys tem, both the hydraulic fluid pump and the hydraulic fluid operated motor can be used at a high specific output. Moreover, the invention results in a decreased compressed air consumption. From another aspect it is an object to provide a control device being a part of such a control system.

For these and other objects I provide a control device for a power system for driving a hydraulic fluid actuated 3,626,695 Patented Dec. 14, 1971 motor, said power system comprising a compressed air actuated motor, a supply conduit to said compressed air actuated motor connected to a source of compressed air, a pump driven by said air actuated motor for supplying pressurized hydraulic fluid to a supply conduit to said hydraulic fluid actuated motor, and a restriction means in said supply conduit to the hydraulic fluid actuated motor causing a pressure drop in the flow of hydrauic fluid, said control device comprising a valve means in said supply conduit to the compressed air actuated motor, and motor means arranged, on the one hand, for urging said valve means into a closing-off or restricting position when the pressure in the supply conduit to said hydraulic fluid actuated motor reaches a certain pressure so as to limit the fluid pressure in the supply conduit to the hydraulic fluid actuated motor, and arranged, on the other hand, for urging said valve means into a closing-elf position when the pressure drop across said restriction means reaches a certain value so as to limit the flow in the supply conduit to the hydraulic fluid actuated motor.

The invention is described in detail with reference to the accompanying drawings in which FIG. 1 is a diagrammatic representation of a power system having a control device according to the invention. FIG. 2 is a diagram on the pressure P and flow Q which drive a hydraulic fluid operated motor illustrated in FIG. 1; FIG. 3 is a longitudinal section through a motor actuated control valve which is schematically illustrated in FIG. 1; FIG. 4 is a longitudinal section through a modified design of a piston means illustrated in FIG. 3, and FIG. 5 is a longitudinal section through a motor actuated control valve which can be used as an alternative to that illustrated in FIG. 3. Corresponding details have been given the same reference numerals in the various figures.

In FIG. 1, reference numeral '11 refers to a compressed air driven motor for instance a sliding vane motor, which is supplied with drive air through a supply conduit 12 connected to a non-illustrated source of compressed air. The supply conduit 12 is controlled by means of a valve 13 which is used both as a restriction valve and as a closeofl valve. The motor 11 is directly connected with a hydraulic fluid pump 14 by means of the drive shaft 15. The pump 15 can be of the sliding vane type as well. The hydraulic fluid pump is supplied with fluid from a tank 16 and it delivers the hydraulic fluid to a hydraulic fluid conduit 17 which is the supply conduit of a hydraulic fluid actuated motor 18.

A restriction 19 is arranged in this supply conduit 17, and upstream of this restriction there is a pressure sensing conduit 20 connected so as to communicate with a pressure chamber 21 in a valve actuating motor 22 with the hydraulic fluid conduit 17. correspondingly, another pressure sensing conduit 23 is connected downstream of the restriction 19 so as to communicate with a second pressure chamber 24 with the hydraulic fluid conduit 17. In the motor 22, a piston 25 is arranged to be slidable in a cylinder 26 andthereby separate the two pressure chambers or cylinder chambers 21, 24 from each other. The valve 13 is spring biased towards an open position by means of a spring 27, as illustrated in the figure, but, by means of a piston rod 28, the piston 25 is adapted to restrict or close the valve 13 against the action of the spring. The piston 25 has also another piston rod 29 which is slidable in a cylinder 30 and acts as a slide or piston in the cylinder with the end face 31 being the piston surface. The cylinder 30 is connected to a tank by means of a control valve :32 and is thus without pressure or, alternatively, by means of the control valve, it is connected through a connecting conduit 33 with the pressure sensing conduit 20, i.e. to the hydraulic fluid conduit 17.

By means of a pre-stressed spring 34, the control valve 32 is spring biased towards the position illustrated in the figure, in which position the cylinder 30 is drained. When, however, the pressure in the conduit 17 attains a certain limit value, for instance if the motor 18 is loaded to the point of stopping, the tension of the spring 34 is overcome, because, through a pressure sensing conduit 35, the control valve 32 is influenced by the pressure in the conduit 17, and the control valve 32 switches into the other posi tion and conveys pressure fluid to the cylinder 30. The piston surface 31 of the slide 29 has such a great area that the pro-stressed spring 27 of the closing-off valve 13 is overcome and the valve 13 thus closes ofl the conduit 12 for supplying drive fluid to the air motor 11. The motor 18 may for instance represent a number of motors such as a rotation motor and a feed motor of a rotary drill of the core drill type using a diamond drill bit. These motors may be alternatively or simultaneously connected. If only a single feed motor in the form of a conventional hydraulic cylinder with a reciprocating piston is connected to the hydraulic fluid conduit 17 and this feed motor reaches an end stop, the control device will come into action as described, and the valve 13 closes. The pressure in the conduit 17 is maintained at the limit value since the valve 13 will open if the pressure in the conduit 17 tends to decrease. In FIG. 2, which is a graphic representation on the pressure P and fiow Q in the hydraulic fluid conduit 17, the limit pressure is illustrated schematically by the line 36. The pressure can thus not exceed this limit value.

If, on the contrary, the motor 18 is unloaded, for instance, in the case of a rotary drill, it is a rotary motor adapted to rotate a drill string or a drill pipe over a chuck and the chuck is not gripping the drill pipe, the speed of the air motor 11 increases, as does the speed of the pump 14. An increased flow Q in the hydraulic fluid conduit 17 results and, thereby, the rotary speed of the motor 18 increases. If this increase in rotary speed were continued freely, the motor 18 and the pump 14 would overspeed until they break down. Since, however, the pressure drop across the restriction 19 is proportional to the square of the flow, the piston 25 will actuate the valve 13 by means of the piston rod 28 to restrict or close the supply conduit 12 when the flow in the conduit 17 increases.

The flow Q will have an upper limit value which is almost independent of the pressure P. This limit value is schematically illustrated by the line 37 in FIG. 2. The limit lines 36 and 37 are chosen to be somewhat inside the maximum pressure and the maximum flow, respectively, which can be permitted in consideration of the components which are part of the hydraulic fluid system. The limit pressure in the conduit 17 for closing the valve 13 may, for instance, be 200 bar, but the pressure loss across the restriction 19 for closing the valve 13 need only be 12% on this pressure. Therefore, the loss in output capacity on account of the restriction is negligible. Since the pressure drop across the restriction is that little, the pressure in the conduit 17 can be sensed either upstream of the restriction 19 as illustrated in FIG. 1 or downstream of it.

The broken line indicated by reference numeral 38 in FIG. 2 shows the characteristic curve of the combination of pressure and flow that would appear in the pressure conduit 17 for a certain combination of air motor, hydraulic pump and drive air pressure, it the control device according to the invention were not arranged to limit the pressure and the flow. On account of the control device, however, approximately, the hydraulic fluid motor 18 will work along the characteristic curve indicated by the solid line 38 and along the limit lines 36 and 37. Unless the limit lines 36 and 37 are somewhat inclined, the power system will be unstable. In practice, there will be such inclinations and the motor 18 will for instance work along the dotted line 38a. The inclinations imply that the pressure limit varies somewhat with the flow and that the flow limit varies somewhat with the pressure.

If a control device according to the invention is not used, one must choose an air motor which has lower output capacity and a characteristic curve of the pressure and the flow in the hydraulic fluid conduit 17 approximately follows the broken line curve 39 in FIG. 2 in order to avoid the pressure and flow exceeding the values permitted. Since the output capacity of the hydraulic fluid motor 18 is the mathematical product of the values of the pressure and the flow of its drive fluid, there will be an output capacity which, in this case, is almost only of the output capacity which is generated in accordance with the characteristic curve 38. In connection with the power system according to the invention, the motor 18 may be an axial piston motor of the swash plate type with automatically variable displacement so that the displacement is increased at a control pressure in the conduit 17 just below the limit pressure 36.

In FIG. 3, there is illustrated the valve 13, the motor 22 and the control valve 32. The valve 32 has a slide 40 which is influenced by the pressure in the conduit 33, which is illustrated in FIG. 1 as two separate conduits; that is to say, the slide is influenced by the pressure in the conduit 20. The closing-ofl valve 13 in the air supply conduit 12 is in the form of a seat valve having a valving member 41 which is influenced, on the one hand, by the spring 27, and, on the other hand, by the piston rod 28. The piston rods 28, 29 are in the form of a single cylindrical rod which has an annular groove in which a split ring 42 is arranged so as to be a stop shoulder for the piston 25 which is slidable on the rod 28, 29. With this arrangement, the piston 25 is not forced to move with the rod or slide 28, 29, when the cylinder 30 is pressurized and, therefore, the valve 13 gets a faster closing action. Moreover, a stop 43 in the cylinder 26 is permitted which limits the movement of the piston 25 so that the valve can not close entirely but only creates a restriction when the flow in the conduit 17 reaches its limit value. However, the valve closes entirely when the pressure reaches its limit value. Reference numeral 45 indicates a drain conduit which drains the cylinder 38 through the valve 32 and also drains a clearance space 46.

In FIG. 4, there is illustrated an alternative design of the piston 25. The piston 25 is integral with the piston rods 28, 29, and a one-way valve 44 is arranged to permit fast movement when the cylinder 30 is pressurized.

In FIG. 5 there is illustrated an alternative design of the motor 22 for actuating the valving member 41. The piston 25 is arranged in a fixed position on the rod 28, 29, and a pressure equalizing passage 47 leads through the rod 28, 29 to an end chamber 48 so as to balance the rod against pressure fluctuations in the valve chamber 49 for the valving element 41. The movement of the piston 25 is affected by the pressure upstream and downstream of the restriction 19 as in FIG. 1 and a control valve 50 of the same type as the control valve 32 has a slide 51 which, like the slide 40, is affected by the pressure in the conduit 20. When the limit pressure is reached, the slide 51 opens a passage 52 so that the hydraulic fluid in the pressure chamber 24 is drained through the drain conduit 45. The conduit 23 must be restricted as illustrated at 53 in order to permit the desired rapid closing of the valve 13.

The embodiments of the control device and its closingoff valve 13, motor 22 and control valves 32, 50 are only to be considered as examples and their details may be modified within the scope of the claims. For instance, the spring 27, which biases the valving element 41, may of course be replaced by an air spring or by a piston which is biased by a constant air pressure, and the piston 25 may be a piston in the form of a membrane. The spring 27 may also be replaced by a spring which is disposed in the cylinder chamber 24 so as to bias the piston 25. The invention is not limited to any particular field of use, but the motor 18 may, for instance, be a hydraulically actuated impact tool or be a hydraulic fluid motor for any other purpose.

I claim:

1. A control device for a power system for driving a hydraulic fluid actuated motor, said power system comprising a compressed air actuated motor, a supply conduit to said compressed air actuated motor connected to a source of compressed air, a pump driven by said air actuated motor for supplying pressurized hydraulic fluid to a supply conduit to said hydraulic fluid actuated motor, and restriction means in said supply conduit to the hydraulic fluid actuated motor causing a pressure drop in the flow of hydraulic fluid, said control device comprising valve means in said supply conduit to the compressed air actuated motor, and motor means arranged on the one hand for urging said valve means into a closing-off position when the pressure in the supply conduit to said hydraulic fluid actuated motor reaches a certain pressure so as to limit the fluid pressure in the supply conduit to the hydraulic fluid actuated motor, and arranged on the other hand for urging said valve means into a closing-off or restricting position when the pressure drop across said restriction means reaches a certain value so as to limit the flow in the supply conduit to the hydraulic fluid actuated motor.

2. A control device according to claim 1 in which said motor means for actuating the valve means includes a first double acting piston means which is balanced with. respect to its piston areas, which piston means separates a first pressure chamber connected to the supply conduit of the hydraulic fluid actuated motor upstream of the restriction means from a second pressure chamber connected to the supply conduit of the hydraulic fluid actuated motor downstream of the restriction means, and which is arranged to urge the valve means towards closed position as a result of fluid pressure working upon the piston surface which works in the first pressure chamber, said motor means for actuating the valve means also including a second piston means arranged to urge the valve means into closed position when loaded by hydraulic fluid, and a control valve is adapted to permit supply of hydraulic fluid from the supply conduit of the hydraulic fluid actuated motor to said second piston means only when the pressure in said supply conduit of the hydraulic fluid actuated motor has reached a limit pressure.

3. A control device according to claim 2 in which said second piston means is a cylindrical rod which is slidably arranged in a cylinder and has one of its end v faces in contact with the valve means, the other end face being the piston surface of said second piston means, and said first piston means being disposed on the cylindrical rod.

4. A control device according to claim 3 in which said cylindrical rod has an axial shoulder which is an axial abutment to the first piston means which is slidably arranged on the cylindrical rod.

5. A control device according to claim 1 in which the motor means for actuating the valve means includes a first double acting piston means which is balanced with respect to its piston areas and which piston means separates a first pressure chamber connected to the supply conduit of the hydraulic fluid actuated motor upstream of the restriction means from a second pressure chamber connected to the hydraulic fluid conduit downstream of the restriction means, said piston means being arranged to urge the valve means towards closed position by means of fluid pressure 'working on the piston surface which works in the first pressure chamber, and a control valve controlled by means of the fluid pressure in the supply conduit to the hydraulic fluid actuated motor, and connected to said second pressure chamber so as to relieve the second pressure chamber of pressure when the fluid pressure in the supply conduit to the hydraulic fluid actuated motor reaches a limit pressure.

6. A control device according to claim 5 in which the piston means has two oppositely directed piston rod means of the same area, one of which extends through said second pressure chamber so as to influence the valve means by means of its end face, and the other of which extends through said first pressure chamber into a compressed air chamber which is in communication with a compressed air chamber in which the end of the first piston rod means is disposed.

7. A control device according to claim 6 in which the two piston rod means consist of a single cylindrical piston rod which extends through the piston means, the piston means being in a fixed position on said piston rod.

8. A control device according to claim 1 in which said valve means is spring biased towards open position.

9. A power system for driving a hydraulic pressure fluid actuated motor comprising a compressed air actuated motor, a supply conduit to said compressed air actuated motor connected to a source of compressed air, valve means in said supply conduit, a supply conduit for supplying drive fluid to said hydraulic fluid actuated motor, a pump driven by said compressed air actuated motor for supplying pressurized hydraulic fluid to said supply conduit to said hydraulic fluid actuated motor, a restriction means in said supply conduit to the hydraulic fluid actuated motor causing a pressure drop in the flow of hydraulic fluid, and motor means arranged on the one hand for urging said valve means into a closing-01f or restricting position when the pressure in the supply conduit to said hydraulic fluid actuated motor reaches a certain pressure so as to limit the fluid pressure in the supply conduit to the hydraulic fluid actuated motor, and arranged on the other hand for urging said valve means into a closing-off or restricting position when the pressure drop across said restriction means reaches a certain value so as to limit the flow in the supply conduit to the hydraulic fluid actuated motor.

References Cited UNITED STATES PATENTS 2,573,993 11/1951 Sedgwick 6052 H.F. X 2,877,624 3/1959 Zoller 6052 H.F. X 3,179,040 4/1965 Seltzer 6052 H.F. UX 3,540,213 11/1970 Johnston et al. 601

EDGAR W. GEOGHEGAN, Primary Examiner 

